Medicines discovery for auditory disorders: Challenges for industry

A comprehensive overview of advanced dynamic in vitro intestinal and hepatic cell culture models

Orally administered drugs pass through the gastrointestinal tract before being absorbed in the small intestine and metabolised in the liver. To test the efficacy and toxicity of drugs, animal models are often employed; however, they are not suitable for investigating drug-tissue interactions and making reliable predictions, since the human organism differs drastically from animals in terms of absorption, distribution, metabolism and excretion of substances. Likewise, simple static in vitro cell culture systems currently used in preclinical drug screening often do not resemble the native characteristics of biological barriers. Dynamic models, on the other hand, provide in vivo-like cell phenotypes and functionalities that offer great potential for safety and efficacy prediction. Herein, current microfluidic in vitro intestinal and hepatic models are reviewed, namely single- and multi-tissue micro-bioreactors, which are associated with different methods of cell cultivation, i.e., scaffold-based versus scaffold-free.

Preclinical prospects of investigational agents for hearing loss treatment

INTRODUCTION

: Hearing loss has a high prevalence, with aging, noise exposure, ototoxic drug therapies, and genetic mutations being some of the leading causes of hearing loss. Health conditions such as cardiovascular disease and diabetes are associated with hearing loss, perhaps due to shared vascular pathology in the ear and in other tissues.

AREAS COVERED

: Issues in the design of preclinical research preclude the ability to make comparisons regarding the relative efficacy of different drugs of interest for possible hearing loss prevention or hearing restoration. This has not slowed the advancement of candidate therapeutics into human clinical testing. There is a robust pipeline with drugs that have different mechanisms of action providing diverse candidate therapies and opportunities for combination therapies to be considered.

EXPERT OPINION

: Much of the preclinical research literature lacks standard study design elements such as dose response testing, and lack of standardization of test protocols significantly limits conclusions regarding relative efficacy. Nonetheless, the many positive results to date have supported translation of preclinical efforts into clinical trials assessing potential human benefits. Approval of the first hearing loss prevention therapeutic is a major success, providing a pathway for other drugs to follow.

Special considerations in the design and implementation of pediatric otoprotection trials

PURPOSE

Cisplatin-induced hearing loss (CIHL) is a common late effect after childhood cancer treatment having profound, lifelong consequences that lower quality of life. The recent identification of intravenous sodium thiosulfate (STS) as an effective agent for preventing pediatric CIHL represents a paradigm shift that has created new opportunities for expanding STS usage and developing additional otoprotectants. The purpose of this paper is to discuss key considerations and recommendations for the design and implementation of future pediatric otoprotection trials.

METHODS

An approach synthesizing published data and collective experience was used.

RESULTS

Key issues were identified in the categories of translational research, trial designs for systemic and intratympanic agents, measurement of ototoxicity, and biostatistical challenges.

CONCLUSIONS

Future pediatric otoprotection trials should emphasize (1) deep integration of preclinical and early-phase studies; (2) an embedded or free-standing design for systemic agents based on mechanistic considerations; (3) use of suitable audiologic testing batteries for children, SIOP grading criteria, and submission of raw audiologic data for central review; and (4) novel endpoints and innovative study designs that maximize trial efficiency for limited sample sizes. Additional recommendations include routine collection of DNA specimens for assessing modifying effects of genetic susceptibility and meaningful inclusion of patient/family advocates for informing trial development.

IMPLICATIONS FOR CANCER SURVIVORS

Changing the historical paradigm from acceptance to prevention of pediatric CIHL through expanded research with existing and emerging otoprotectants will dramatically improve quality of life for future childhood cancer survivors exposed to cisplatin.

Noise-induced hearing disorders: Clinical and investigational tools

A series of articles discussing advanced diagnostics that can be used to assess noise injury and associated noise-induced hearing disorders (NIHD) was developed under the umbrella of the United States Department of Defense Hearing Center of Excellence Pharmaceutical Interventions for Hearing Loss working group. The overarching goals of the current series were to provide insight into (1) well-established and more recently developed metrics that are sensitive for detection of cochlear pathology or diagnosis of NIHD, and (2) the tools that are available for characterizing individual noise hazard as personal exposure will vary based on distance to the sound source and placement of hearing protection devices. In addition to discussing the utility of advanced diagnostics in patient care settings, the current articles discuss the selection of outcomes and end points that can be considered for use in clinical trials investigating hearing loss prevention and hearing rehabilitation.

Development and Characterization of an In Vitro Round Window Membrane Model for Drug Permeability Evaluations

Hearing loss and balance disorders are highly common disorders, and the development of effective oto-therapeutics remains an area of intense research. Drug development and screening in the hearing research field heavily rely on the use of preclinical models with often ambiguous translational relevance. This often leads to failed advancement in the market of effective therapeutics. In this context, especially for inner ear-specific pathologies, the availability of an in vitro, physiologically relevant, round window membrane (RWM) model could enable rapid, high-throughput screening of potential topical drugs for inner ear and cochlear dysfunctions and could help accelerate the advancement to clinic and market of more viable drug candidates. In this study, we report the development and evaluation of an in vitro model that mimics the native RWM tissue morphology and microenvironment as shown via immunostaining and histological analyses. The developed three-dimensional (3D) in vitro model was additionally assessed for barrier integrity by transepithelial electrical resistance, and the permeability of lipophilic and hydrophilic drugs was determined. Our collective findings suggest that this in vitro model could serve as a tool for rapid development and screening of topically deliverable oto-therapeutics.

Prevention of Noise-Induced Hearing Loss Using Investigational Medicines for the Inner Ear: Previous Trial Outcomes Should Inform Future Trial Design

Significance: Noise-induced hearing loss (NIHL) is an important public health issue resulting in decreased quality of life for affected individuals, and significant costs to employers and governmental agencies. Recent Advances: Advances in the mechanistic understanding of NIHL have prompted a growing number of proposed, in-progress, and completed clinical trials for possible protections against NIHL via antioxidants and other drug agents. Thirty-one clinical trials evaluating prevention of either temporary or permanent NIHL were identified and are reviewed. Critical Issues: This review revealed little consistency in the noise-exposed populations in which drugs are evaluated or the primary outcomes used to measure NIHL prevention. Changes in pure-tone thresholds were the most common primary outcomes; specific threshold metrics included both average hearing loss and incidence of significant hearing loss. Changes in otoacoustic emission (OAE) amplitude were relatively common secondary outcomes. Extended high-frequency (EHF) hearing and speech-in-noise perception are commonly adversely affected by noise exposure but are not consistently included in clinical trials assessing prevention of NIHL. Future Directions: Multiple criteria are available for monitoring NIHL, but the specific criterion to be used to define clinically significant otoprotection remains a topic of discussion. Audiogram-based primary outcome measures can be combined with secondary outcomes, including OAE amplitude, EHF hearing, speech-in-noise testing, tinnitus surveys, and patient-reported outcomes. Standardization of test protocols for the above primary and secondary outcomes, and associated reporting criterion for each, would facilitate clinical trial design and comparison of results across investigational drug agents. Antioxid. Redox Signal. 36, 1171-1202.

Noise-Induced Hearing Loss and its Prevention: Current Issues in Mammalian Hearing

Noise-induced hearing loss (NIHL) has been well investigated across diverse mammalian species and the potential for prevention of NIHL is of broad interest. To most efficiently develop novel therapeutic interventions, a good understanding of the current state of knowledge regarding mechanisms of injury is essential. The overarching goals of this review are to 1) concisely summarize the current state of knowledge, and 2) provide opinions on the most significant future trends and developments.

Noise-induced hearing loss and its prevention: Integration of data from animal models and human clinical trials

Animal models have been used to gain insight into the risk of noise-induced hearing loss (NIHL) and its potential prevention using investigational new drug agents. A number of compounds have yielded benefit in pre-clinical (animal) models. However, the acute traumatic injury models commonly used in pre-clinical testing are fundamentally different from the chronic and repeated exposures experienced by many human populations. Diverse populations that are potentially at risk and could be considered for enrollment in clinical studies include service members, workers exposed to occupational noise, musicians and other performing artists, and children and young adults exposed to non-occupational (including recreational) noise. Both animal models and clinical populations were discussed in this special issue, followed by discussion of individual variation in vulnerability to NIHL. In this final contribution, study design considerations for NIHL otoprotection in pre-clinical and clinical testing are integrated and broadly discussed with evidence-based guidance offered where possible, drawing on the contributions to this special issue as well as other existing literature. The overarching goals of this final paper are to (1) review and summarize key information across contributions and (2) synthesize information to facilitate successful translation of otoprotective drugs from animal models into human application.

Use of the guinea pig in studies on the development and prevention of acquired sensorineural hearing loss, with an emphasis on noise

Guinea pigs have been used in diverse studies to better understand acquired hearing loss induced by noise and ototoxic drugs. The guinea pig has its best hearing at slightly higher frequencies relative to humans, but its hearing is more similar to humans than the rat or mouse. Like other rodents, it is more vulnerable to noise injury than the human or nonhuman primate models. There is a wealth of information on auditory function and vulnerability of the inner ear to diverse insults in the guinea pig. With respect to the assessment of potential otoprotective agents, guinea pigs are also docile animals that are relatively easy to dose via systemic injections or gavage. Of interest, the cochlea and the round window are easily accessible, notably for direct cochlear therapy, as in the chinchilla, making the guinea pig a most relevant and suitable model for hearing. This article reviews the use of the guinea pig in basic auditory research, provides detailed discussion of its use in studies on noise injury and other injuries leading to acquired sensorineural hearing loss, and lists some therapeutics assessed in these laboratory animal models to prevent acquired sensorineural hearing loss.

Noise-induced hearing loss: Translating risk from animal models to real-world environments

Noise-induced hearing loss (NIHL) is a common injury for service members and civilians. Effective prevention of NIHL with drug agents would reduce the prevalence of NIHL. There are a host of challenges in translation of investigational new drug agents from animals into human clinical testing, however. Initial articles in this special issue describe common pre-clinical (animal) testing paradigms used to assess potential otoprotective drug agents and design-related factors that impact translation of promising agents into human clinical trials. Additional articles describe populations in which NIHL has a high incidence and factors that affect individual vulnerability. While otoprotective drugs will ultimately be developed for use by specific noise-exposed populations, there has been little effort to develop pre-clinical (animal) models that accurately model exposure hazards across diverse human populations. To facilitate advances in the translational framework for NIHL otoprotection in pre-clinical and clinical testing, the overarching goals of the current series are to (1) review the animal models that have been used, highlighting the relevance to the human populations of interest, (2) provide insight into the populations for whom pharmaceutical interventions might, or might not, be appropriate, and (3) highlight the factors that drive the significant individual variability observed in humans.